OKLAHOMA CITY (AP) — A bill approved by the Republican-led Oklahoma Legislature this year that seeks to crack down on protesters is unconstitutional and would chill the ability of groups to mobilize people to advocate for racial justice, a civil rights group argues in a federal lawsuit filed Monday.

The Oklahoma chapter of the NAACP filed the lawsuit in federal court in Oklahoma City, along with the national NAACP, the nation's oldest civil rights organization, and the Institute for Constitutional Advocacy and Protection at Georgetown University Law Center.

The lawsuit argues the law, which ta...